1st make sure your using an obd1 code reader it may have an obd2 style port but its not its obd 1 then you need to check the wiring if thats good then it needs a pcm
it is behind the water pump in front of timing chain cover driven by cam
to be honest you will get more power wit a natural asperated 350 then a blown 305 the motor just sucks for getting power no disrepect. you will spend 6000 dollars for just about 100 hp you can but a stroked 350 ready to go for 4000 bucks with over 550 hp cjeck jegd a summit racing for complete engines use the 305 for a boat anchor
Either 145 with the base 305 4bbl or 165 with the 305 Crossfire injection option
A Y-body is a Corvette, an F-body is a Camaro/Firebird
the ss stands for super sport and rs stands for rally sport ... z28 .... your guess is as good as mine , ss is the best in my eyes .